This invention relates generally to apparatus for cooling computer subsystems and, more particularly, to such apparatus that reduce or eliminate the need for fans or other devices for moving air.
Heat dissipation is an important consideration in the design of modern-day computer subsystems, especially as the power levels of such subsystems continue to grow. Major sources of heat in such subsystems include microprocessors and hard disk drive assemblies. Future microprocessor modules incorporated into workstations and into server applications are expected to dissipate 150 to 200 watts each. A typical multi-processor system incorporating 32 microprocessors is expected to dissipate 10 to 12 kilowatts. Similarly, future hard disk drive assemblies incorporated into such workstations and server applications are expected to dissipate more than 25 watts each. Many of such workstations and servers will incorporate multiple hard disk drive assemblies in close proximity to each other, thus posing a significant thermal cooling challenge.
In the past, computer subsystems of this kind have incorporated within their enclosures cooling devices such as heat sinks and air movers in the form of fans. Air volume flow rates on the order of 2.5 to 5 liters/second, at a velocity of 2 to 3 meters/second, typically have been required for each microprocessor.
As the power levels of such computer subsystems have increased, it has become increasingly difficult to adequately cool the subsystems' power dissipating components. Generally, such cooling has been achieved by increasing the air mass flow rates and by applying extended surfaces to disk drive assemblies. Large multi-processor systems and large multi-disk drive systems used in dedicated computer rooms can be cooled by moving air at high mass flow rates, and the resulting acoustic noise generally can be tolerated. Multi-processor and multi-disk systems used in office environments, on the other hand, must meet more stringent acoustic emission guidelines and regulations, as well as customer/user requirements. In these cases, cooling the systems by increasing the air mass flow rates is not considered a practical option.
A further consideration is that high-end servers housing multiple microprocessors, associated memory devices, and ASICs, and/or housing multiple hard disk drive assemblies, ordinarily will require compact physical packaging to meet performance goals. This requirement, of course, conflicts with the requirement to efficiently cool the systems' power dissipating components.
Some efforts have been made in the past to cool electronic systems using a working fluid that undergoes a reversible phase change. Specifically, power dissipating components such as power transistors have been mounted directly to an external panel of such systems, and a sealed fluid channel is formed in the panel for carrying the working fluid. The working fluid absorbs heat by evaporating in the portion of the fluid channel adjacent to the power transistors, and it releases heat by condensing in other portions of the fluid channel.
Although the cooling apparatus described briefly above has been effective in cooling power transistors mounted in the manner described, the apparatus has not proven to be entirely satisfactory. Specifically, the design configuration has not proven to be sufficiently versatile to efficiently cool power dissipating components that are mounted in positions other than directly on an external panel. Such components can include microprocessors mounted on a printed circuit board and hard disk drive assemblies
It should, therefore, be appreciated that a need remains for an apparatus for effectively cooling more of a computer subsystem's power dissipating components, without exceeding acoustic emission guidelines and regulations, and without exceeding reasonable constraints on the subsystem's physical size. The present invention fulfills this need and provides related advantages.